This kind of thing happens all the time.

Some people are even entirely conscious of their products "humble beginnings". Bungie (the guys behind Halo) made a little game for mac called "Gnop". Take a wild guess as to what that was.

Ill give you a hint

Go ahead and make your game, there's no shame in releasing it. The only thing you shouldn't do is make it look and work exactly the same as a commercially copy-written product, so even just swapping some graphics around should get you mostly in the clear. Just to be sure though, find at least one thing to innovate (again, I know easier said than done) to completely set your game apart, and your very much good to go again

Good luck!

The only thing you shouldn't do is make it look and work exactly the same as a commercially copy-written product,

That's gonna be quite hard to do unless I turn it into some kind of puzzle game, and right now that's not the direction I was after . I never played the original game, but I'm pretty sure my clone won't have too many innovations in it compared to the original (at least I haven't thought of that many things to add yet and I bet they already added my yet un-added twists in the original, since the game itself imposes some limits).

I don't see how you could feel your work has been immoral.

Would you say the same thing if I tried to put it on fgl for sale?

If you're not using someone elses code or assets and the price you charge is reasonable then thats fine.

I'd be willing to bet a couple of hundred bucks that popcap wasn't first either. (They weren't first with bejeweled atleast, that gameplay is almost identical to a mid 1990s DOS game)

If you're not using someone elses code or assets and the price you charge is reasonable then thats fine.

... or someone else's trademarked name.

I obviously don't plan on using the same name, code or assets as the original, but in terms of gameplay it will probably come out pretty much like the original. I mean, what can you add in that game besides the obvious bombs, clear the row, clear the column, clear all the same "jewels" from the board, block a row and block a column? And I bet they have that in the original as well

you can also use a different board size, tiles that can't be removed, tiles that only get removed if you clear a tile next to them, a bonus that allows you to make more than one move at once or one to convert all tiles of one color to a different randomly selected color.

You could reverse the game (rather than starting with a filled board you could start with an empty board and have tiles appear one row at the time from the bottom, changing the goal of the game to be more like tetris (prevent the board from filling up),

you could let your tiles have both colors and symbols allowing the player to clear using either 3 of the same symbol or 3 of the same color. (and give bonus points or special effects (clear surrounding tiles for example) if both color and symbol matches).

There is a virtually unlimited number of directions you can take the basic concept and mechanics in, not all ideas and directions are good and not all will be fun when combined but there is definitely room to twist the concept into something unique.